private void PinOne_TextChanged(object sender, TextChangedEventArgs e)
 {
     if (PinOne.Text.Length > 0)
     {
         PinTwo.Focus();
     }
 }
 private void PinThree_TextChanged(object sender, TextChangedEventArgs e)
 {
     if (PinThree.Text.Length > 0)
     {
         PinFour.Focus();
     }
     else
     {
         PinTwo.Focus();
     }
 }